The invention relates to a mass spectrometer, and preferably a quadrupole mass spectrometer, having a power supply resonant circuit.
Mass spectrometers, and especially quadrupole mass spectrometers, require for their operation, depending on their construction and mass range, voltages of from a few hundred to a few thousand volts with frequencies of a few megahertz. These operating voltages are produced, generally by resonant circuits, because only a very low effective power is required. The mass-spectrometer system itself, including the quadrupole electrodes, plugs, conductors, etc., constitutes the resonant circuit capacity. The frequency of the operating voltage is an important operating parameter, affecting the separation of operating ions passing through the mass spectrometer. It is therefore usually set by controlling the resonant circuit with a quartz-crystal-controlled oscillator.
Furthermore, to achieve good efficiency, the quality factor of the resonant power circuit is usually high. This, however, increases the danger that even slight detuning of the circuit will produce large changes. Such detuning occurs when, for example, cables or measuring heads of the mass spectrometer are changed because these are part of the capacity of the resonant power circuit. Also, aging and temperature effects produce such detuning. Even keeping the amplitude of the high-frequency alternating current stable by means of a regulating circuit does not result in any appreciable improvement, since the detuning has an effect on the curve shape and thus adversely affects the sensitivity of a quadrupole mass spectrometer.
To avoid these difficulties, it is known to equip the high-frequency operating-power generator for a quadrupole mass spectrometer with a manually-operated equalizer for maintaining the resonance. A disadvantage of this is that such adjustment can only be performed by highly skilled persons. When the apparatus is used by persons with inadequate training and knowledge of the physical processes involved in a mass spectrometer, there is therefore always the danger of inaccurate or even erroneous results.